This invention relates to a new and improved active bandpass filter and, in particular, the application thereof in a receiver and signalling system.
Current practice in bandpass active filters uses the "POLE and ZERO" mathematical concept to design a multistage filter. In these cases, the practical individual stage gain is limited to approximately five times and the "Q" of the stage is normally limited to about 25. Information on prior art active filters can be found in the book "Active Filters" by Don Lancaster, Howard W. Sams, Division of Macmillan Inc.
The use of a bridged "T" network as a bandpass elimination filter or notch filter is well known. This network is able to eliminate a particular frequency, and circuits of this type are described in "Reference Data for Radio Engineers" by ITT.